1. Field of the Invention
The present invention relates to a suspension arm of a vehicle, and particularly to a welded structure in a suspension arm.
2. Description of the Related Art
As a suspension arm of a vehicle, there has been conventionally known a hollow suspension arm in which outer peripheral ends of an upper plate member and a lower plate member, which each have a U-shaped cross section, are joined together by welding (see Patent Document 1, for example).
[Patent Document 1] Japanese Patent Application Laid-open No. 6-143953
In recent years, weight saving of the whole vehicle has been strongly required in order to improve fuel efficiency, reduce exhaust gas, and improve motion performance. One solution for the weight saving of a suspension arm is to form the arm with thinner plate members, but reduction of the fatigue strength of the base material due to the thinning of the arm should be avoided. Since stresses often concentrate around a weld end near a lower ball joint attached to the suspension arm, the fatigue strength of the base material around the weld end needs to be particularly ensured.